1. Field of the Invention
The present invention relates to a method of forming an ohmic contact layer and a method of forming a metal wiring in a semiconductor device using the ohmic contact layer. More particularly, the invention relates to a method of forming an ohmic contact layer using an electrode-less plating process and a method of forming metal wiring in a semiconductor device using the ohmic contact layer.
2. Description of Related Art
As contemporary semiconductor devices become more highly integrated their constituent components are reduced in size. This is true for the gate electrodes and source/drain regions forming a transistor. Unfortunately, as the channel length separating source/drain regions decreases to match the reduced line width of the transistor's gate electrode, the performance characteristics of the transistor begin to degrade.
As constituent components shrink in size, the properties of various materials once used to form the components must be re-evaluated. For example, wiring used to connect the source/drain regions of a transistor were formerly made from polysilicon. However, densely integrated semiconductor devices suffer from operating speed issues and excessive power consumption requirements when conventional polysilicon wiring is used due to a corresponding high contact resistance or a high sheet resistance.
In attempts to address this problem, metal wiring has been used as a replacement for polysilicon wiring in contemporary semiconductor devices. Generally speaking, conventional metal wiring includes a tungsten plug and a composite layer including titanium. However, the fabrication processes used to form the titanium composite layer and the tungsten plug must be separately performed and typically require different types of fabrication equipment. This requirement significantly slows fabrication throughput for the semiconductor device. Additionally, undesired impurities may be diffused into the substrate supporting the semiconductor device during the fabrication process used to form the titanium composite layer due to its high processing temperature.
In view of these drawbacks, another method of forming metal wiring has recently been proposed. This method includes forming an ohmic contact layer from tungsten, forming a barrier layer from tungsten nitride, and forming a plug from tungsten. This alternate method offers greater simplicity of implementation over previous approaches to the fabrication of metal wiring.
Figures (FIGS.) 1 and 2 are cross-sectional views illustrating a conventional method of forming metal wiring. FIG. 3 is a scanning electron microscope (SEM) picture showing a cross-sectional view of an overgrown tungsten silicide layer resulting from the conventional method of forming metal wiring.
Referring to FIG. 1, an insulating interlayer layer formed on a substrate 10 is etched to form an insulating interlayer pattern 20 including a contact hole 15 exposing an upper surface of substrate 10.
Referring to FIG. 2, a composite layer 30 is formed with a substantially uniform thickness on the exposed surface of substrate 10 and insulating interlayer pattern 20. More particularly, a tungsten layer 26 and a tungsten nitride layer 28 are successively stacked to form composite layer 30. Then, the remaining portion of contact hole 15 is filled with tungsten to form a tungsten plug 40.
According to this method, composite layer 30, including tungsten layer 26 and tungsten nitride layer 28, and tungsten plug 40 may be formed in situ, and the metal wiring may be formed at a lower temperature than the temperature usually required to form the former titanium composite layer.
However, in the above method, the tungsten layer 26 is commonly formed using a chemical vapor deposition (CVD) process incorporating (e.g.,) tungsten fluorine (WF6) gas. Unfortunately, a tungsten bearing gas may excessively react with the silicon in substrate 10 to form a tungsten silicide layer. For example, FIG. 3 shows an overgrown tungsten silicide layer caused by an excessive reaction of the tungsten in a tungsten bearing gas with silicon.
Additionally, when a titanium nitride layer (not illustrated) is formed as a capping layer before forming tungsten layer 26, the tungsten bearing gas may permeate the capping layer so that a tungsten silicide layer is formed on silicon substrate 10.